Method of and apparatus for analysis of the composition of a sample by electron spin resonance (ESR) spectrometry employing carrier suppression

Abstract

Described is an electron spin resonance (ESR) spectrometer comprising a miniaturized radio-frequency (RF) microwave cavity resonator. The miniaturized RF microwave cavity resonator receives a carrier signal from a circulator, modulates the signal path signal, and reflects the carrier signal back to the circulator to amplify the carrier signal prior to demodulation. A mixer receives and demodulates the carrier signal and outputs an audio signal to generate an ESR spectrum for analyzing a chemical composition of a fluid sample. The ESR spectrum represents a magnetic susceptibility of the fluid sample to a magnetic resonance cause variation in a resonant frequency of the miniaturized RF microwave cavity resonator. In a desired aspect, the carrier signal is split into two paths prior to demodulation. The two paths are demodulated by different mixers to produce two separate outputs, an absorption spectrum and a dispersion spectrum.

What is claimed is: 
     
       1. An electron spin resonance (ESR) spectrometer for analyzing the composition of a sample comprising:
 a radio frequency (RF) or microwave source for generating a carrier signal; 
 a power splitter for splitting the carrier signal into a reference path signal and a signal path signal; 
 a circulator for receiving the signal path signal and a digital phase shifter for receiving the reference path signal; 
 a miniaturized RF microwave cavity resonator, wherein the miniaturized RF microwave cavity resonator receives the signal path signal from the circulator, modulates the signal path signal, and reflects the signal path signal back from the circulator to amplify the signal path signal prior to demodulation; and 
 a pair of mixers, wherein a first mixer demodulates the signal path signal and a second mixer demodulates the reference path signal to produce an absorption spectrum and a dispersion spectrum which are used to generate an ESR spectrum for analyzing the composition of a sample received by the miniaturized RF microwave cavity resonator; 
 wherein the ESR spectrum represents a magnetic susceptibility of the sample causing a variation in a resonant frequency of and reflected signal from the miniaturized RF microwave cavity resonator. 
 
     
     
       2. The ESR spectrometer as set forth in  claim 1 , further comprising a mixer for receiving and demodulating the signal path signal and outputting an audio signal to generate an ESR spectrum for analyzing the composition of the sample, wherein the ESR spectrum represents a magnetic susceptibility of the sample causing a variation in a resonant frequency of and a reflected signal amplitude from the miniaturized RF microwave cavity resonator. 
     
     
       3. The ESR spectrometer as set forth in  claim 2 , further comprising a first mixer and a second mixer for receiving the reference path signal and the signal path signal as inputs, respectively, and outputting a first audio signal and a second audio signal. 
     
     
       4. The ESR spectrometer as set forth in  claim 3 , wherein an amplitude of the first audio signal contains an absorption spectrum and an amplitude of the second audio signal contains a dispersion spectrum. 
     
     
       5. The ESR spectrometer as set forth in  claim 4 , wherein the signal path signal reflected from the miniaturized RF microwave cavity resonator detects an audio modulation at a frequency that is the same frequency as a modulation coil around the miniaturized RF microwave cavity resonator. 
     
     
       6. The ESR spectrometer as set forth in  claim 5 , wherein the reference path signal and the signal path signal are split by a first 90° hybrid coupler and a second 90° hybrid coupler, respectively, prior to being received by the first mixer and the second mixer. 
     
     
       7. The ESR spectrometer as set forth in  claim 6 , wherein the second 90° hybrid coupler comprises an additional ninety degrees of phase length to allow the first mixer and the second mixer to generate different outputs. 
     
     
       8. The ESR spectrometer as set forth in  claim 7 , wherein an algorithm is employed to automatically lock a voltage controlled oscillator (VCO) to the miniaturized RF microwave cavity resonator. 
     
     
       9. The ESR spectrometer as set forth in  claim 8 , wherein a VCO control switch allows a tuning port of the VCO to be controlled by a digital-to-analog converter (DAC) or a phase detector integrator. 
     
     
       10. The ESR spectrometer as set forth in  claim 9 , wherein when a phase difference between the signal path signal and the reference path signal is at an optimal value, the phase detector integrator will lock the VCO to the miniaturized RF microwave cavity resonator. 
     
     
       11. A method of using electron spin resonance (ESR) spectrometry Liar analyzing the composition of a sample, comprising acts of:
 generating a carrier signal; 
 splitting the carrier signal with a power splitter, wherein the carrier signal is split into a reference path signal and a signal path signal; 
 receiving of the signal path signal by a circulator and the reference path signal by a digital phase shifter; 
 receiving of a sample by a miniaturized RF microwave cavity resonator; 
 receiving the signal path signal from the circulator by the miniaturized RF microwave cavity resonator; 
 modulating the signal path signal; 
 reflecting the signal path signal back from the circulator to amplify the signal path signal prior to demodulation; and 
 demodulating the signal path signal and the reference path signal by a pair of mixers to produce an absorption spectrum and a dispersion spectrum which are used to generate an ESR spectrum for analyzing the composition of the sample; 
 wherein the ESR spectrum represents a magnetic susceptibility of the sample causing a variation in a resonant frequency of and reflected signal from the miniaturized RF microwave cavity resonator. 
 
     
     
       12. The method of using ESR spectrometry as set forth in  claim 11 , further comprising acts of:
 receiving and demodulating of the signal path signal by a mixer; and 
 outputting an audio signal to generate an ESR spectrum for analyzing the composition of the sample, wherein the ESR spectrum represents a magnetic susceptibility of the sample causing a variation in a resonant frequency of and a reflected signal amplitude from the miniaturized RF microwave cavity resonator. 
 
     
     
       13. The method of using ESR spectrometry as set forth in  claim 12 , further comprising acts of:
 receiving the reference path signal as an input by a first mixer; 
 receiving the signal path signal as an input by a second mixer; and 
 outputting a first audio signal and a second audio signal. 
 
     
     
       14. The method of using ESR spectrometry as set forth in  claim 13 , further comprising acts of:
 synchronously demodulating an absorption spectrum from the first audio signal; and 
 synchronously demodulating a dispersion spectrum from the second audio signal. 
 
     
     
       15. The method of using ESR spectrometry as set forth in  claim 14 , wherein the signal path signal reflected from the miniaturized RF microwave cavity resonator detects an audio modulation at a frequency that is the same frequency as a modulation coil around the miniaturized RF microwave cavity resonator. 
     
     
       16. The method of using ESR spectrometry as set forth in  claim 15 , further comprising an act, of splitting of the reference path signal and the signal path signal by a first 90° hybrid coupler and a second 90° hybrid coupler, respectively, prior to being received by the first mixer and the second mixer. 
     
     
       17. The method of using ESR spectrometry as set forth in  claim 16 , further comprising an act of employing an algorithm to automatically lock a voltage controlled oscillator (VCO) to the miniaturized RF microwave cavity resonator. 
     
     
       18. The method of using ESR spectrometry as set forth in  claim 17 , further comprising an act of using a VCO control switch to allow a tuning port of the VCO to be controlled either by a digital-to-analog converter (DAC) or a phase detector integrator. 
     
     
       19. The method of using ESR spectrometry as set forth in  claim 18 , further comprising an act of using, the phase detector integrator to lock the VCO to the miniaturized RF microwave cavity resonator when a phase difference between the signal path signal and the reference path signal is at an optimal value.